"Down syndrome." Encyclopædia Britannica. Encyclopædia Britannica Online School Edition. Encyclopædia Britannica, 2010. Web.16 Nov. 2010 http://www.school.eb.com/eb/article-293387.
"Down syndrome." The Gale Encyclopedia of Science. Ed. K. Lee Lerner and Brenda Wilmoth Lerner. 4th ed. Detroit: Gale, 2008. Gale Science In Context. Web. 16 Nov. 2010.
"Down syndrome." Encyclopædia Britannica. Encyclopædia Britannica Online School Edition. Encyclopædia Britannica, 2010. Web.16 Nov. 2010 http://www.school.eb.com/eb/article-293387.
"Down syndrome." The Gale Encyclopedia of Science. Ed. K. Lee Lerner and Brenda Wilmoth Lerner. 4th ed. Detroit: Gale, 2008. Gale Science In Context. Web. 16 Nov. 2010.
The National Down Syndrome Society. (2010). NDSS. Retrieved November 17, 2010, from http://www.ndss.org/index.php